I took on an LG dishwasher for a friend, don't usually do LG DWs, and i'm having some problems with it.

The complaint was no draining and it wasn't. Never got an error though. It would push the water column slowly up to the dispose-all but just enough for a trickle. It would eventually drain the machine with two cancel/drains (5minutes +-).

I pulled the unit out, turned it upside down, changed the pump, changed the weird shaped sump gasket , changed the filter assy with the two fragile gaskets, and blew out the hose, put it all back together and still the same trickle.

I took the sump apart the second time, but just the top part that the top and middle spray arm tube is attached to and started a drain and noticed a boiling action around the entry port for the drain pump - like the pump was running fine but not pushing water out the hose. Put it back together and did several drains and once noticed that water seemed to be pushing back up into the machine and coming out the filter area in the middle.

Using my years of shad tree experience......
1) Check the Air Gap on top the sink for grit/crud. Clean as necessary.
2) Pull drain hose off of the garbage disposer, use your finger or screw driver to look for crude at the Garbage Disposer drain inlet nipple.
3) If you still have a drain problem, get a hose and hook it to the DW pump (drain) and the other end to a open bucket. If it drains now, you know the hose in the cabinet is blocked.
4) If no drain...I‘d look at the pump again.
5) You might want to look at the high water level cut off switch inside the dish cabin, to see if it is messed up ...but I’m starting to reach a little here.
6) Hope this helps some.

The blow-through test on drain hose can be deceiving especially if you're using compressed air and not the lip lock method. For example, I have seen the cute plumber's trick where they add in a drain hose extension and crank the hell out of the clamp so that it all but completely shuts off the flow thru the drain hose. The end result was no draining.

So, the moral of the story is to run the dishwasher in drain mode with a piece of hose connected at the discharge going into a bucket or pot so that you can see the discharge stream in action.

Thanks for the replies...
I actually used the lip-lock method to blow out the drain hose - ick.
However! I didn't see any back flow preventer in the drain hose
Do those things get chewed up and spat out?

John63; there really should be a check valve in the hose? LG LDS5811?
Is it in the pump end of the hose or deeper inside it?

There's a black check valve in the drain sump but, as far as i can tell, it goes on a hose that goes back into the sump from the drain pump area...

There's a small check valve inside of the drain hose---where it connects to the sump assy (drain body). Over time---this small black / rubber valve *can* become dislodged and drain into the sink disposer (or sink drain). It is not really necessary to replace the drain hose if it is missing as long as the drain hose has a *loop* which elevates the drain hose higher than the discharge connection of the sink disposer.

If the impellers are not damaged and the DRAIN MOTOR runs...

If the DRAIN HOSE is clear...

If you're 100% positive that the DRAIN HOSE is not kinked / crimped *anywhere*...

If the discharge connector of the SUMP ASSY is clear and the anti-drainback rubber flapper is not stuck (water flows into pump body thru this discharge hole) and no food or glass shards obstruct this hole...

Thanks for the posts everyone and John63 thanks for the tip about the check-valve in the drain hose. Got the part in. Went back to the scene.
Flipped that sucker on it's top.
Carefully extracted my previously replaced perfectly good pump.
Slapped his old pump back on.
Changed out the old toothless drain hose.
Put on the new gray drain hose with intact check valve.
Did the 180 on the machine and stuck it back in the cave.
And it f___in worked.

A piece of glass (i'm guessing) cut out most of the old flapper.

Sorry, maybe too much hops at this point, but who woulda thunk?
The check valve is in the drain hose.... ¿